1. Field of the Invention
The present invention relates to zoom lenses suited to lens-shutter cameras, video cameras and the like and, more particularly, to zoom lenses having with a movable lens unit of positive refractive power disposed closest to the object side and a lens unit of negative refractive power disposed closest to the image side.
2. Description of Related Art
Recently, the use of aspherical zoom lenses has prevailed in lens-shutter cameras, video cameras and the like with the results that the number of lens members is reduced, the total length of the entire lens system is shortened, and the structure of construction is simplified. Accordingly, compact zoom lenses, while still extending the zooming range, have been increasing in variety.
Of these zoom lenses, such as a simple zoom lens for a lens-shutter camera, there have been proposed a number of two-unit zoom lenses, each of which consists of, in order from the object side, a first lens unit of positive refractive power and a second lens unit of negative refractive power, totaling two lens units, wherein the first and second lens units each axially move in differential relation to vary the focal length with the total length being kept relatively short.
Such two-unit zoom lenses have been proposed in, for example, Japanese Laid-Open Patent Applications No. Sho 56-128911, No. Sho 57-201213, No. Sho 60-170816, No. Sho 60-191216, No. Sho 62-56917, No. Hei 2-50118, No. Hei 2-71220, No. Hei 2-190812 and No. Hei 4-145408.
Now, of the various aberrations, chromatic aberrations are corrected by combining lenses made of glass materials which differ from each other in dispersion. Besides this correction method, there is another method of correcting the chromatic aberrations of a lens by introducing a diffractive optical element, as the diffractive optical element is formed on a refractive surface of the lens or on a parallel flat plate of the lens. Such a diffraction-refraction type of optical system has previously been proposed in, for example, Japanese Laid-Open Patent Applications No. Hei 4-213421, No. Hei 6-324262, No. Hei 9-197274 and No. Hei 9-211329.
In particular, in the above Japanese Laid-Open Patent Application No. Hei 9-211329, there is disclosed a two-unit zoom lens consisting of a first lens unit of positive refractive power and a second lens unit of negative refractive power, wherein one diffractive optical element is used in the second lens unit. Also, in the above Japanese Laid-Open Patent Application No. Hei 9-211329, it is suggested that a plurality of diffractive optical elements may be used in the second lens unit, but, nothing more is taught about how to apply, for example, two diffractive optical elements to the second lens unit to improve the performance of the zoom lens.